Generally, an airbag refers to a vehicle safety device for providing protection to the occupants during a frontal vehicle collision at an impact speed of about 40 km/h or above by deploying explosive chemicals to generate a gas and inflate the airbag cushion upon sensing a crash with a crash impact sensor.
The requirements for airbag fabrics are low air permeability to facilitate airbag unfolding, high strength and high thermal resistance to protect the airbag from damage or rupture, and high flexibility to reduce impacts on occupants.
Particularly, an airbag for automobile, manufactured in a defined dimension, can be folded into the steering wheel, the door panel, and so forth in the vehicle to reduce its volume to the minimum and then inflated to unfold when the inflator is in operation.
It is therefore of a great importance that the airbag fabric secures good mechanical properties, good folding property, and high flexibility to reduce impacts on the occupants, with a view to effectively maintaining folding and packing properties of the airbag while packing the airbag into the vehicle, preventing damage or rupture of the airbag, achieving high performance of unfolding airbag cushions and minimizing impacts on occupants. In fact, there have never been suggested airbag fabrics capable of maintaining excellences in air sealing effect and flexibility for the occupant's safety, sufficiently enduring impacts on the airbag, and being packed into a vehicle effectively.
Conventionally, polyamide fibers such as nylon 66 have been used as a material for airbag fabric. Despite high impact resistance, nylon 66 is inferior to polyester fibers in regard to resistance to heat and humidity, light resistance, and dimensional stability, and more expensive.
Japanese Patent Publication No. Hei 04-214437 discloses the use of polyester fibers overcoming these problems. However, the use of the conventional polyester fiber in the manufacture of an airbag leads to difficulty in packing the airbag into a small space in a vehicle due to extremely high stiffness, excessive thermal shrinkage during heat treatment at high temperature due to high elasticity and low elongation, and limitations in maintaining good mechanical properties and unfolding performance under severe conditions of high temperature and high humidity.
Accordingly, there is a need for developing a fiber capable of maintaining good mechanical properties and air sealing effect to be suitable for use in airbags for vehicle and providing high flexibility to reduce impacts on occupants, good packing property, and an ability to maintain good mechanical properties under severe conditions of high temperature and high pressure.